This paper deals with a dynamic pricing using the H∞ control with uncertain behavior in electricity market trading. The dynamic pricing is a decision procedure of an electricity price based on power supply and demand balance in power grids. However, in a future deregulated electricity market, both power consumers and generators determine their own power demand and supply selfishly according to the price information. Moreover, uncertainties are also included in their behavior. For this problem, we propose a novel price decision method using the locational price-updating H∞ controllers. This paper shows a design process of this price-updating H∞ controller to evaluate the following performance to reduce supply-demand imbalances in power grids and the robustness against uncertainties in electricity market participants' behavior, respectively. In addition, this paper also shows the effectiveness of our proposed price decision method using the designed H∞ controller through numerical simulation results.